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• Restoring corrupted video after recovery

  22 août 2019, par Harold.Demure

  I have recently recovered the content of an old drive of mine using photorec.

  To my surprise, photorec recovered a lot of files with non-video extensions (.sqlite, .apple, .pdf, .torrent...) that contain fragments of video. I can see these fragments only using mplayer/mencoder (quicktime and vlc cannot). Some of the files are even hundreds of megabyte large, but mplayer only shows me a few seconds of the video.

  Is there any script/data carving tool that I can use to see if I can recover more video fragments from these files ? I am not afraid of trying solutions that require some coding or manual inspection (e.g., search for headers via hex editors).

  Thank you for your help, any suggestion is highly appreciated.
  Harol.

• Compressing videos from a smartphone

  21 septembre 2019, par fejesjoco

  I have a Nexus 6p with the stock camera. It’s set to record at 1080p, 30fps. Here’s a 5 second sample (11 MB).

  Videos from this phone come out at about 17 Mbps on average. I tried to compress it with ffmpeg with -c:v libx264 -crf 23 -preset veryslow, the result comes out at about 5.5 MB, which is about 9 Mbps.

  I think this bitrate is a bit too much. When I look at torrent file listings, I can see high quality videos at 3 GB in size on average, and if such a movie is 90 minutes long on average, that is about 4-5 Mbps which sounds okay.

  I’m wondering, why the big difference ? I can notice that my video is noisy/grainy (which is expected from a phone), and that might reduce compressibility. I tried a few ffmpeg filters, like hqdn3d and atadenoise, but the noise mostly remained (maybe I didn’t play with it enough). Then I figured, the video is also shaky (which is also expected), and that might reduce compressibility too (and even makes temporal noise filtering less effective). I tried to stabilize it with the deshake filter, but that didn’t help either.

  I know I could just limit the bandwidth to whatever I like, but there must be a reason why ffmpeg thinks it needs a high bandwidth to maintain a certain quality, and a lower bandwidth would just decrease the quality.

  Why do these videos have such a high bitrate ? What’s the best way to compress them more while keeping or even increasing their quality ?

• Impossible to redirect video stream after conversion (mkv to mp4)

  17 décembre 2019, par elgrusko

  I’m currently realising a school project which aims a streaming video website (like Netflix) using torrent-stream (with the magnet link). I am using NodeJS for the stream part.

  My problem is : I can’t redirect the stream to the HTML 5 player while i’m trying to stream and converting (with ffmpeg) video at the same time. I think it’s because I just can’t know what’s will be the final size of the converted file.
  In browser’s console I have this message : net::ERR_CONTENT_LENGTH_MISMATCH 200 (OK)

  I tried to put this in the header : Transfer-Encoding: chunked instead of Content-Length
  I specify that the stream (before conversion) works perfectly

  This is my code :

  getTorrentFile.then(function (file) {
  
                  res.setHeader('Content-Type', 'video/mp4');
  
                  res.setHeader('Content-Length', file.length);
  
                  const ranges = parseRange(file.length, '15' /* variable à comprendre */, { combine: true });
  
                  console.log(ranges);
  
                  if (ranges === -1) {
  
                      // 416 Requested Range Not Satisfiable
  
                      console.log('416')
  
                      res.statusCode = 416;
  
                      return res.end();
  
                  } else if (ranges === -2 || ranges.type !== 'bytes' || ranges.length > 1) {
  
                      // 200 OK requested range malformed or multiple ranges requested, stream ent'ire video
  
                      if (req.method !== 'GET') return res.end();
  
                      console.log('200')
  
                      stream = file.createReadStream()
  
                      ffmpeg(stream)
  
                      .videoCodec('libx264')
  
                      .audioCodec('aac')
  
                      .output(res)
  
                      .output('./video/' + film + '_s' + season + '_e' + episode + '.mp4')
  
                      .outputFormat('mp4')
  
                      .outputOptions('-movflags frag_keyframe+empty_moov')
  
                      .on('error', function(err) {
  
                          console.log('An error occurred: ' + err.message);
  
                      })
  
                      .on('progress', function(progress) {
  
                          console.log('Processing: ' + progress.targetSize + 'kb done');
  
                        })
  
                      .on('end', function() {
  
                          console.log('Processing finished !');
  
                      })
  
                      .addOutputOption('-acodec')
  
                      .run()

  Sorry if i’m not really clear, ask me some questions if you need more informations :)

  Thanks for your help, bye :)